Composite material

ABSTRACT

The invention relates to a composite material consisting of a base body with a multilayered coating, containing at least one mulitphase layer of aluminum oxide, zirconium and/or hafnium and titanium and a single-phase layer made of AI 2 O 3 , ZrO 2  and/or HfO 2 .

The invention relates to a composite material of a base body with a multi-layer coating. Such composite bodies are, for example, used as cutting inserts for machining purposes, namely, turning, milling or boring. The base bodies, to which the coating can be applied by physical or chemical vapor deposition processes (PVD or CVD), can be composed of hard metal, a cermet, steel or a ceramic.

DE 27 36 982 A1 already describes a wear resistant coating for shaped parts, especially for tools, comprised of a shaped body, preferably of hard metal, and one or more surface coatings, at least one of which is a protective layer with a ceramic matrix into which a further material is incorporated. The ceramic matrix and the material incorporated therein have different coefficients of thermal expansion so that the protective layer is subject to the formation of fine microcracks therein. Unstabilized and/or partially stabilized ZrO2 has been proposed as the material incorporated into the interstices of a ceramic matrix of Al₂O₃. To produce such a layer by the CVD process, AlCl₃, CO₂ and H₂ are admitted as a gas phase into a reaction vessel at 1100° C. to produce Al₂O₃ or ZrCl₄ and water vapor (H₂O) are admitted to produce ZrO₂. Because of the density difference between the tetragonal modification of ZrO₂ formed at temperatures above the transformation temperature of about 1100° C. and the monoclinic modification formed below about 1100° C., with a corresponding phase conversion there can be a significant change in volume of the deposited ZrO₂. As a consequence, with increasing volume proportions of the ZrO₂ there is a simultaneous increase in the microcrack density in the deposited ceramic layer.

In DE 28 25 009 C2, a hard metal body with a thin wear-resistant surface layer of Al₂O₃ has been described and which is composed completely or at least 85% of the κ-modification and any possible remainder of the α-modification, forming surface regions or patches at most 10 μm in size. The aluminum oxide layer can contain further additions of titanium, zirconium and/or hafnium. To create this ceramic layer by the CVD process, the gas mixture apart from AlCl₃, CO₂, CO and H₂ has also small amounts of 0.03 to 0.5% TiCl₄ added to it. This addition, however, serves exclusively or nearly exclusively for the formation of the κ-Al₂O₃ phase.

A further CVD process for depositing Al₂O₃ and/or ZrO₂ using additional reagents, like hydrogen sulfide, has been described in EP 0 523 021 B1.

DE 195 18 927 A1 describes a coated cutting tool comprised of a substrate of sintered carbide or ceramic with a wear-resistant composite ceramic coating which has two different metal oxide phases, for example of Al₂O₃ and ZrO₂ and in addition thereto a doping agent selected from the group of sulfur, selenium, tellurium, phosphorus, arsenic, antimony, bismuth or compounds of these elements. To produce this two-phase layer by a CVD process, for example AlCl₃ and ZrCl₄, CO₂ with H₂ as a carrier gas, in addition to an H₂S gas, is passed over the substrate body at a temperature of about 700° to 1250° C. and a pressure from 133 Pa to ambient pressure, whereby the two-phase layer with the doping agent is deposited.

EP O 786 536 A1 describes a coated hard metal body with a 3 to 30 μm thick aluminum oxide coating which has been deposited by means of CVD and/or PVD and contains 0.005 to 0.5 weight % chlorine. Optionally 0.5 to 10 weight % Zr and/or Hf and 1.5 to 15 weight % Ti can be contained in this coating.

EP 0 162 656 A2 describes a multilayer coating on a hard metal substrate body which is comprised of an inner layer, which is composed of at least one carbide, nitride, carbonitride, carbo-oxygen nitride, oxynitride, boron nitride or boron carbo nitride of titanium, and an outer multilayer coating with a total thickness of 5 to 20 μm and provided with an outer layer of a plurality of Al₂O₃ coatings with a respective thickness of 0.01 to 2 μm and each comprised of an Al₂O₃ film in which titanium oxide has been dissolved or which has been codeposited with at least 30 volume percent titanium oxide. The layers are separated by intervening layers with respective thicknesses of 0.01 to 2 μm and which each can comprise TiC, TiN, TiCN, TiCNO, TiNO, titanium oxides, Ti(B,N), Ti(B,N,C), SiC, AlN or AlON.

In WO 00/17 416, a composite material of a coated hard metal or cermet base body has been described on which the single layer or a multilayer coating is applied at least in the form of a 0.5 μm to 25 μm thick coating and preferably the outermost phase is an Al₂O₃ phase containing a ZrO₂ and/or HfO₂ phase which in turn contains a third fine dispersive phase consisting of an oxide, oxycarbide, oxynitride or oxycarbonitride of titanium. The proportion of the third phase in the overall composition of this layer amounts to 0.2 to 5 mol %. To produce such a three phase layer, a CVD process with deposition temperatures between 900° C. and 1000° C. is selected in which the gases required for the deposit contain chlorides of the Al, Zr and Hf, and in addition CO₂, H₂, CH₄ and N₂ or inert gas under pressures of 10 to 100,000 Pa. The TiO_(x) incorporated as the third phase has a positive effect on the growth speed and on the particle sizes of the aluminum oxide and zirconium or hafnium oxide. Preferably a coating temperature of 960° C. is selected in which the ZrO₂ is present in the monoclinic form. From the mentioned publication, therefore, hard metal substrate bodies are known which have layer sequences TiN—Ti(C,N) and the described three phase layer.

It is the object of the present invention to provide a composite body which, when used as a cutting insert, affords increased cutting effectivity as well as a longer useful life. Higher cutting effectiveness is determined in terms of the desired high cutting speeds and increased thicknesses of the chip removed. If possible such cutting inserts should be usable in so-called dry cutting operations.

These objects are attained with a composite material according to claim 1. Further features of the invention are described in the dependent claims.

The basic idea of the present invention is that of using on a base body at least one multiphase coating of the oxides of aluminum, zirconium and/or hafnium and of titanium (as a three phase coating) and a single phase layer or coating of Al₂O₃, ZrO₂ or HfO₂. In the coating on the base body, therefore, there is both at least one mutiphase oxide layer as well as at least one single phase oxide layer. The multiphase layer can, apart from the three mentioned oxide components, contain MgO and the single phase layer can additionally contain up to 1% of a titanium oxide proportion. According to a further feature of the invention, however, at least two and preferably at least three layers are provided of which each is comprised of the mentioned multiphase layer of the oxides of Al, Zr, Ti and/or Al, Hf, Ti and/or Al, Zr, Ti, Mg and/or Al, Hf, Ti, Mg, and a single phase oxide layer of an oxide of Hf, Zr or Al. Preferably at least three-phase or four-phase oxide layers are provided between which respective single phase oxide layers are disposed and whereby a single phase oxide layer also forms the outer cover coating. These layers have a fine grained lattice structure and a uniform phase distribution and provide a high degree of thermal insulation. The base body can also be comprised of a hard metal, a cermet, or steel or a ceramic material.

Between the substrate body and the first oxide layer which preferably is a multiphase oxide layer is at least one layer of a carbonitride of titanium, hafnium, zirconium. This cover layer can have a thickness between 2 to 15 μm, especially 3 to 8 mm.

According to a further feature of the invention it is possible to provide, between the multiphase oxide layer and the single phase oxide layer, preferably in a multi layer sequence of the multiphase oxide layers and single phase oxide layers between each of the mentioned layers, one or more intermediate layers of titanium, hafnium or zirconium carbonitride.

These intervening layers have preferably a thickness between 0.2 and 3 μm, especially of 2 μm.

The total thickness of all multiphase oxide layers and all single phase oxide layers preferably lies between 6 and 20 μm especially at 10 μm. The difference of a single phase oxide layer can amount to 2 to 6 μm preferably 4 μm and the thickness of an individual single phase oxide layer can amount to 1 to 5 μm, preferably 3 μm.

The multiphase coating is produced by a CVD process which is basically known from WO 00/17 416 or as the so-called middle temperature CVD process.

In a further embodiment of the invention, to eliminate tensile stresses or to increase compressive stresses in the composite body, the composite body can be subjected to a treatment with a blasting agent, the blasting agent being preferably composed composed of a hard metal granulate which can have a substantially rounded grain configuration and a maximum grain diameter of 200 μm and more preferably of a maximum of 100 μm.

Further advantages of the invention are described in connection with an exemplary embodiment. The drawing shows.

FIGS. 1 to 3 respective diagrams which provide information with respect to the improved life of the composite material according to the invention in cutting inserts by comparison with the state of the art.

The test objects were in all three cases cutting inserts of the type CNMG120412-5. In all three cases the substrate body was a hard metal (THM) but the coatings were different in the three cases. In a first test series the work press was gray cast iron with a cutting speed of 450 m/min and a cutting depth of 2.5 mm and an advance of the cutting insert of 0.315 mm per revolution. The first cutting body was comprised of a hard metal base body coated with a two layer coating of TiCN—Al2O3 (as an outer layer). The life achieved was less than 2 min. A significantly improved life was given with a two layer coating in which on a TiCN— cover layer a is three phase oxide layer according to WO 00/17 416 was applied comprised of Al₂O₃/ZrO₂/TiO_(x).

A clear improvement in the useful life still further can however be achieved with a cutting insert which had a TiCN adjacent the substrate body and a six layer outer coating which was comprised of three individual layers each of a three phase oxide coating and a single phase ZrO₂ layer.

In a second test a gray cast iron workpiece with an extremely rough surface is machined by turning whereby in comparison to the previously described test only the cutting speed was reduced to 200 m/min. Based upon this cutting speed, there was obtained a useful life of 6 min for the cutting inserts with a TiCN—Al₂O₃ coating, of about 7 min for cutting inserts with a TiCN—Al₂O₃/ZrO₂/TiO_(x) coating, and a useful life of 9 min for a cutting insert with the coating of the invention in which by contrast with the previously described versions had a three times alteration of a three-phase oxide layer of Al₂O₃/HfO₂/TiO_(x) and the single phase oxide layer of HfO₂. The above described cutting tests were carried out with so-called dry cutting.

As FIG. 3 shows, however, with use of a lubricant coolant, still higher useful lives can be obtained. In the lathe turning of grey cast iron at cutting speeds of 450 m/min, a cutting depth of 2.5 mm, and a feed of 0.315 mm per revolution, the useful life of the cutting insert with a TiCN—Al₂O₃ cutting amounted to about 4.5, min, the useful life of a cutting insert with a coating according to WO 00/17 416 was about 6.5 min, whereas the coating according to the invention resulted in useful lives of 10 or 12.5 min. Especially when HfO₂ forms the single phase oxide layers, it is possible to obtain a still more substantial increase in the useful life by comparison with the already improved life using ZrO₂ as the single phase oxide layer. All coatings were applied by the so-called CVD-MT (middle temperature) proc3ess under the same process conditions. 

1. A composite material of a base body with a multilayer coating which has at least one multiphase layer of aluminum, zirconium and/or hafnium oxides and a single phase layer of Al₂O₃, ZrO₂ or HfO₂.
 2. A composite material according to claim 1 characterized in that the multiphase layer contains an additional proportion of MgO and/or the single phase layer contains up to 1% of an additional titanium oxide proportion.
 3. The composite material according to claim 1, characterized by at least two, preferably at least three, layers which are comprised each of a multiphase layer of oxides of Al, Zr, Ti and/or Al, Hf, Ti, and/or Al, Zr, Ti, Mg and/or Al, Hf, Ti, Mg and of a three phase oxide layer of Hf, Zr or Al.
 4. The composite material according to claim 1 characterized in that the base body is composed of a hard metal, steel, cermet or ceramic.
 5. The composite material according to claim 1 characterized in that between the substrate body and a first oxide layer, which preferably is a multiphase oxide layer, at least one layer of TiCN, HfCN or ZrCN is provided which preferably has a thickness of 1 to 15 μm, especially 3 to 8 μm.
 6. The composite material according to claim 1 characterized in that between the multiphase oxide layer and the single phase oxide layer, preferably between each two such layers, one or more intermediate layers are provided of TiCN, HfCN, or ZrCN, each of which preferably has a thickness between 0.2 μm to 3 μm, especially 2 μm.
 7. The composite material according to claim 1 characterized in that the total thickness of all of the multiphase oxide layers and all single phase oxide layers is 6 to 20 μm, preferably 10 μm, whereby further preferably the thickness of an individual multiphase oxide layer is 2 to 6 μm, preferably 4 μm, and/or the thickness of the individual single phase oxide layer is 1 to 5 μm, preferably 3 μm.
 8. The composite material according to claim 1 characterized in that the multilayer coating is produced by means of CVD.
 9. The composite material according to claim 1 characterized in that the composite material is subjected to a final dry blast treatment with using a granular blast agent composed of a high metal granulate and which at least in major part has a rounded grain configuration with a maximum diameter of 150 μm preferably with a maximum of 100 μm. 